| 摘要 |
PURPOSE:To avoid the erroneous reception of the undesired signal produced by the spurious even when an FM broadcast is received in an intensive field region, by reducing a high frequency gain of a front end by means of a muting pulse for a receiver using a phase locking loop. CONSTITUTION:When the signal level is less than a prescribed value at amplifying/wave detecting part 3, a pulse is delivered from an A/D converter 9 and supplied to a terminal 6 of a control circuit 7. The pulse width is increased by delaying only the fall time with the same rise time through the circuit 7. Then a muting pulse of a large width is delivered through a terminal C of the circuit 7 and applied to a muting circuit 4 to eliminate the noises which are under sweeping. This muting pulse is applied also to an input terminal 13 of an AGC control circuit 6. Thus a transistor Q3 is kept on for a period during which the muting pulse is applied to lower the AGC output down to a level divided by a resistance R9 and a volume VR2. Therefore the high frequency gain of a front end 2 is lowered less as the AGC output is reduced. |
